Hydraulic elevating unit for lifting appliances



y 1969 e. M. DUGELAY 3,455,211

HYDRAULIC ELEVATING UNIT FOR LIFTING APPLIANCES 3 Sheets-Sheet 1 Filed Jan. 23. 1967 M II Mam, m ww ATTOENEYS y 5, 1969 5. M. DUGELAY' 3,455,211

HYDRAULIC ELEVATING UNIT FOR LIFTING APPLIANCES Filed Jan. 23, 19s? a Sheets-Sheet z a 78 4 v /m INVENTOE ATTORNEYS July 15, 1969 e. M. DUGELAY 3,455,211

HYDRAULIC ELEVATING UNIT FOR LIFTING APPLIANCES 3 Sheets-Sheet 5 Filed Jan. 23, 1967 mm 6% mm mm mmwmmh R kw .wm mm mm m m \m on LI- mm a... n I [A R .a W 1 Q j .e Si. 2 R. 2 3v 3 .26 3 5 mm .3 3 w Fm M ATTOENfiY Int. Cl. B66f 3742; F15b 13/04 U.S. Cl. 91--447 6 Claims ABSTRACT OF THE DISCLOSURE A hydraulic elevating unit, specifically for a lift truck, having a housing containing a fluid reservoir, a lifting jack and pump means. Valve means controls the flow of fiuid between the pump means, the jack and the reservoir. The valve means is self-contained within a separate valve block which is readily and removably received within a recess formed in the housing.

This invention relates to a hydraulic elevating unit for lifting appliances, in particular for handling trucks such as low-lift pallet trucks, of a type comprising in a same body a lifting jack and a pump for supplying said jack with fluid under pressure from a reservoir by means of a valve system consisting of a suction valve, a delivery valve and, additionally, a valve for limiting the flow of fluid from the jack to the reservoir and in that direction.

The objects of the invention are to simplify the construction of hydraulic elevating mechanisms, to improve their operation, to reduce the risks of failure and to facilitate the replacement of valves so that, should such replacement prove necessary, any immobilization of the appliance over long periods of time is avoided.

To this end, the elevating unit according to the invention is especially characterized in that said valve system is housed in a single valve-carrier block which is removably fitted in said body independently of the pump and of the jack.

In a preferred form of execution of the invention, the suction valve, the delivery valve and the flow-limiting valve are mounted in central alignment along the axis of the valve-carrier block which is simply inserted in a corresponding recess of the body of the elevating unit and held in position by a locking screw which is screwed in said body.

An axial push-rod is interposed with play in a manner known per se between the suction valve and the delivery valve, said suction valve being subjected to the action of a coaxial operating push-rod provided at one end of a threaded control rod which is screwed coaxially into an internally threaded portion of the valve-carrier block whilst the other end of said control rod extends outwards from the body of the elevating unit and is rigidly fixed to an operating pedal whereby the rotational movement of said control rod can be produced either in one direction or in the other, with the result that said operating push-rod exerts a thrust on the suction valve and this latter in turn exerts a thrust on the delivery valve by means of the intermediate axial push-rod; the two valves aforesaid can thus be lifted from their seats one after the other by producing suitable action on the operating pedal in order that a continuous communication may successively be established in a manner known per se between the pump and the reservoir, then between the jack and the reservoir.

The lifting jack and the pump are mounted vertically one behind the other in a manner known per se in the body of the elevating unit and said valve-carrier block is preferably disposed horizontally, the axis of said block States Patent being located in the plane defined by the axes of the jack and of the pump, the operating pedal being located at the front end of the device, which is of particular interest when the body of the elevating unit performs a pivotal movement relative to the frame of the lifting appliance, as is the case with low-lift pallet trucks.

Further properties and advantages of the invention will become apparent from the following detailed description of one form of execution of the invention as applied to a low-lift pallet truck which is given by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a simplified view in side elevation of the lowlift pallet truck;

FIG. 2 is a front view;

FIG. 3 is a sectional view on a larger scale showing the elevating unit;

FIG. 4 is a sectional view on a still larger scale and showing the valve-carrier block.

The low-lift pallet truck is a well-known handling machine which consists of a small truck provided with fork arms which are intended to be introduced underneath a load or a pallet and to lift the load slightly for the purpose of displacing it over short distances.

The low-lift pallet truck which is shown in FIGS. 1 and 2 is mainly of conventional design. It comprises a lifting carrier constituted by a two-arm fork 1 which rests at the front end on carrier rollers 2, the two fork arms being joined together at the rear end by a bridge 3 which is supported on an elevating unit 4, said elevating unit being carried on guide wheels 5.

As can more readily be seen from FIGS. 3 and 4, the elevating unit 4 comprises in a same body 6 a lifting jack 7 and a pump 8 whereby said jack is supplied with fluid under pressure from a reservoir 9 by means of a valve system which will be described hereinafter. The jack 7 and pump 8 are disposed vertically behind each other. The bridge 3 is supported on the elevating unit 4 by means of a pivot-pin 7b fitted in the projecting end of the plunger 7a of the jack 7 and is thus pivotally coupled to said plunger.

The axle of the guide-wheels 5 is secured to the lower end of the cylinder of the jack 7 which thus serves as a pivot for the rotation of the complete elevating unit and guide wheels within the vertical center-bearing of a crossmember 10' which is coupled to the lifting carrier as will be explained below.

A drawbar 11 terminates at its free end in a handle 12 and terminates at its other end in a yoke 13 which is pivotally mounted on the body 6 of the elevating unit by means of aligned horizontal pins 14 around which are fitted restoring springs 15 which tend to lift the drawbar 11 to the vertical position. Inside the yoke 13, a link-arm 17 in the form of a stirrup is pivotally mounted on aligned horizontal pins 16, said link-arm being pivoted at the top of the stirrup on the projecting end of the plunger 8a of the pump 8. It is thus apparent that, by lowering and raising the drawbar 11, it is possible by means of the link-arm 17 to initiate the reciprocating motion of the plunger 8a of the pump 8. The drawbar 11 additionally serves to pull or to push the pallet truck and to direct this latter by turning the guide wheels 5 together with the elevating unit about the axis of the jack 7 within the vertical center-bearing of the cross-member 10.

One end of an elbowed lever 18 which is pivoted at 19 on the bridge 3 of the lifting carrier is pivotally mounted at 10a on each side of the cross-member 10. The other end of said elbowed lever is coupled by means of an articulated link-rod 20 which extends along the corresponding arm 1 of the lifting arm to one end of another elbowed lever 21, the corresponding carrier roller 2 being mounted on the other end of said lever 21. It is apparent that, if the plunger 7a of the lifting jack 7 is moved upwards as a result of the action of the pump 8, the articulation 7b of the bridge 3 is moved away from the articulations 10a of the elbowed levers 18, thereby initiating the movement of rotation of said elbowed levers about their pivot-pins 19, said movement of rotation being transmitted to the elbowed levers 21 by the articulated linkrods 20, with the result that the lifting carrier rises parallel to itself in a manner which is well-known per se.

In order to lower the lifting carrier, it is necessary to permit the fluid contained in the chamber of the jack 7 to return to the reservoir 9; and in order to prevent any overpressure in the jack chamber which might otherwise be caused by uncontrolled movements of the drawbar, especially during transportation of the load, it is advisable to provide for a neutral position of the elevating unit in which the pump delivers directly into the reservoir.

The elevating mechanisms of low-lift pallet trucks of known types are usually provided for the purpose referred-to above with a system of valves an ancillary components which are usually complicated.

In accordance with the invention, the system of valves and means which are necessary in order to pump fluid under pressure into the lifting jack chamber for the purpose of elevating the load, to return said fluid to the reservoir for the purpose of lowering; the load and, in the neutral position, to discharge fluid from the pump directly into the reservoir, are disposed in alignment in a single valve-carrier block 22 which is removably mounted in the body 6 of the elevating unit, independently of the pump 8 and jack 7. Said valve-carrier block 22 which is simply fitted into a recess 23 of corresponding shape of the body 6 is disposed horizontally, the axial line of valves being located in the plane which is defined by the axes of the jack and of the pump. Said block is held in position by a threaded bushing 24 or locking ring which screws into an internally threaded portion of the recess 23.

The valve-carrier block 22 comprises successively a first chamber 25, a second chamber 26 and a third chamber 27, the first chamber being connected to the second chamber by way of a duct 28 and the second chamber being connected to the third chamber by way of a duct 29.

The chamber has an internal screw-thread 30 in which is screwed a threaded portion 31a of a control rod 31 followed by a bore 32 in which is slidably fitted a cylindrical bearing surface 31b of the control rod 31, said cylindrical bearing surface 31b being fitted with a sealing ring 33. The control rod 31 terminates at the end of the cylindrical bearing surface 31b in an operating push-rod 310 which passes into the duct 28.

The opening of the duct 28 within the chamber 26 forms a seat for the ball 34 of a suction valve, said ball being applied against this valve-seat by a compression spring 35.

The opening of the duct 29 within the chamber 27 forms a seat for the ball 36 of a delivery valve. Said ball 36 is held to its seat by a compression spring 37 which is applied against the base of a sleeve 38. Said sleeve abuts against a recessed stop-collar 39 and is slidably fitted within said chamber 27 with relatively substantial radial play. The base of said sleeve is pierced by a calibrated orifice 40- whilst the opposite open end of the sleeve can be applied in fluid-tight manner about the seating of the ball 36 in opposition to the action of a spring 37. Said sleeve constitutes a flow-limiting valve, the function which will be explained hereinafter.

The intermediate push-rod 41 which passes through the duct 29 is interposed with play between the ball 34 of the suction valve and the ball 36 of the delivery valve.

An operating pedal 42 which is capable of taking up a position of inclination towards the left (FIGURE 2), a horizontal position and a position of inclination towards the right is keyed on the end of the control rod which extends outwardly from the valve-carrier block 22 in front of the body 6 of the elevating unit. The operation of the pedal 42 from its left-hand inclined position to its right-hand inclined position has the eifect of screwing the control rod into the internally threaded portion 30 of the valve-carrier block and consequently of initiating the axial forward motion of the operating push-rod 31c.

In the position shown in the drawing, in which the operating pedal is inclined towards the left, the operating push-rod 310 does not bear on the ball 34 and both the suction and delivery valves are normally applied against their seats by their respective springs.

The chamber 26 opens on the exterior of the valvecarrier block through a lateral opening closed by a detachable cover.43 which is pierced by a hole 44. Said chamber 26 communicates with the chamber 46 of the pump 8 through said hole 44 and through a duct 45 which is pierced in the body 6.

Th recess 23 is fully of revolution and it will be noted that it can be formed inside the body 6 by means of a machining operation which is both very simple and inexpensive. The valve-carr-ier block 122 closely conforms to the shape of said recess except for a portion in which a chamber 47 is formed between said block and the body 6. The chamber 25 communicates with chamber 47 through opening 48 and with the reservoir 9 through a duct 49. Fluid-tightness between the chamber 47 and the exterior is ensured by means of an O-ring seal 50 which is interposed between the valve-carrier block 22 and the body 6. The chamber 27 communicates with the chamber 52 of the jack 7 through a duct 51 of the body 6.

In order to ensure correct orientation within the body 6, the valve-carrier block 22 is provided with two lugs 53 which fit inside the chamber 47 and between which the end of a set-screw 54 is inserted.

The position shown in the drawing is that in which the lifting carrier (fork arms) of the pallet truck can be lifted together with the load which is supported thereon by actuating the pump 8 by means of the drawbar 11 through the intermediary of the link-arm 17. In fact, a downward movement of the pump plunger St: has the effect of forcing the liquid from the pump chamber 46 to the jack chamber 52 via the duct 45, the chamber 26, the duct 29, the chamber 27 and the duct 51, the result of the fluid pressure being to apply the ball of the suction valve 34 against its seat while at the same time lifting the ball of the delivery valve 36 from its seat. The upward motion of the pump plunger 8a produces a partial vacuum within the chamber 26, with the result that the ball of the suction valve 34 is displaced from its seat and the ball of the delivery valve 36 is applied against its seat. As a consequence, the liquid contained in reservoir 9 flows into the pump chamber 46 through the duct 49, the chamber 47, the duct 48, the chamber 25, the duct 28, the chamber 26 and the duct 45, whilst the fluid which was previously fed into the jack chamber 52 remains imprisoned therein and, under the pressure exerted by the load, forcibly applies the ball of the delivery valve 36 against its seat. Each downward movement of the pump plunger 8a will accordingly have the effect of lifting the jack plunger 7a to a slightly greater extent.

In order to place the hydraulic unit in the neutral position to permit the free operation of the drawbar 11 without thereby producing an overpressure within the jack chamber 52, it is merely necessary to place the operating pedal 42 in the horizontal position, thereby causing the operating push-rod 31c to move forward over a short distance. The push-rod accordingly displaces the ball of the suction valve 34 from its seat without producing any action on the ball of the delivery valve 36. A continuous communication is then established between the pump chamber 46 and the reservoir 9 by way of the duct 45, the chamber 26, the duct 28, the chamber 25, the duct 48, the chamber 47 and the duct 49. Inasmuch as the delivery valve 36 is not influenced, the jack plunger 7a remains in the top position which it has assumed.

In order to permit the downward motion of the jack plunger 7a for the purpose of depositing the load being transported, it is merely necessary to actuate the pedal 42 once again and to place this latter in the position of right-hand inclination, thereby having the effect of causing the control plunger 310 to move forward to a further extent. The ball of the suction valve 34 then exerts a thrust on the intermediate push-rod-41 which releases the ball of the delivery valve 36 from its seat. A communication is then established between the jack chamber 52 and the reservoir 9 by way of the duct 51, the chamber 27, the duct 29, the chamber 26, the duct 28, the chamber 25, the duct 48, the chamber 47 and the duct 49.

If the load carried by the jack is not considerable, the fluid which returns from the jack chamber 52 to the reservoir 9 flows through the chamber 27 both through the calibrated orifice 40 of the base of the sleeve 38 and through the free annular space around said sleeve. On the contrary, if the load carried is of a high order, the flow rate of the fluid tends to increase and the pressure of the fluid has the effect of forcing back the sleeve 38 in opposition to the action of the spring 37, with the result that the open end of the sleeve is applied in fluid-tight manner about the seating of the delivery valve 36. Con sequently, the fluid can then flow only through the calibrated orifice 40, thereby limiting the flow rate and slowing down the downward motion of the jack plunger and of the load being carried.

It is apparent that the construction and operation of the elevating mechanism are extremely simple. It will also have been noted that all of the moving parts which control the circulation of fluid are contained in a removable block or unit which can be withdrawn and replaced immediately inasmuch as it is merely necessary for this purpose to unscrew and re-screw the threaded sleeve 24 either from or into the recess 23. In particular, no valve seat is cut in the elevating unit body 6. In the event of failure, the valve-carrier block 22 can be replaced immediately by a new standard element without thereby entailing the need of immobilizing the pallet truck for a long period of time. It will also be noted that the operating pedal 42 is located at the front end of the elevating mechanism and not at the side of this latter. Said pedal is thus readily accessible irrespective of the angular position of the elevating unit as a whole and of the guide wheels of the pallet truck. This feature avoids accidents which would otherwise be liable to arise if the pedal were placed on the side of the elevating unit, if it were required in such a case to operate the pedal when this latter has been brought between the elevating unit and the lifting fork or platform of the pallet truck as a result of the pivotal motion of the guide wheels.

The valve-carrier block 22 is advantageously made of plastic as a single unit in which the cover 43 can be inserted by elastic deformation.

The invention is obviously not limited to the form of execution which has been described in the foregoing and for which any detail modifications can be contemplated without thereby departing either from the scope or the spirit of the invention.

What we claim is:

1. A fluid-actuated elevating unit, in particular for lowlift pallet trucks comprising:

a housing having a recess formed therein;

lifting jack means mounted on said housing for movement in response to the application of a pressurized fluid to said jack means;

pump means mounted on said housing for supplying pressurized fluid to said lifting jack means;

a reservoir formed in said housing for containing a supply of fluid therein;

passageway means formed in said housing and communicating between said lifting jack means, said pump means and said reservoir;

a valve block having valve means for controlling the flow of fluid through said passageway means, said valve block being removably receivable within the recess in said housing, said valve block being independent of the pump means and of the lifting jack means and having a threaded opening formed therein;

said valve means having a suction valve member mounted within said valve block and controlling the flow of fluid from said reservoir to said pump means, a delivery valve member mounted within said valve block and controlling the flow of pressurized fluid from said pump means to said lifting jack means, and a flow control valve member mounted within said valve block and controlling the flow of fluid from the lifting jack means to the reservoir;

push-rod means movably mounted within said valve block between said suction valve member and said delivery valve member with the opposite ends of said push-rod means being adapted to coact with the suction valve member and the delivery valve member, respectively, for assisting in controlling the movement thereof;

a control member having a threaded portion received within the threaded opening formed in said valve block and having an end portion adapted to coact with said suction valve member for controlling the movement thereof, rotational movement of said control member within said threaded opening causing the end portion of said control member to move toward and away from said suction valve member;

a manually actuatable, rotatable opearting member positioned exteriorly of said valve block and interconnected to said control member for effecting rotational movement of said control member whereby the operation of said valve means can be manually controlled; and

securing means connected to said housing and to said valve block for holding same in position within said recess, said valve block being easily detached from said securing means and easily removed from said housing.

2. An elevating unit according to claim 1, wherein said housing has means defining first and second vertically extending bores, said pump means including a reciprocable piston member slideably received within said first bore and said lifting jack means including a reciprocating lift member slideably received within said second bore;

said recess in said housing extending horizontally of said housing and being positioned adjacent the lower ends of said bores; and

said valve block having a central longitudinal axis extending horizontally of said recess and of said housing with said suction valve member, said delivery valve member and said flow control valve member being in axial alignment along said longitudinal axis.

3. An elevating unit according to claim 1, wherein the valve block includes first, second and third chambers and a first duct connecting said first chamber to said second chamber and a second duct connecting said second chamber to said third chamber, said first chamber being in communication with said threaded opening whereby said control member extends into said first chamber for coacting with said suction valve member, said suction valve member being positioned within said second chamber for controlling the flow of fluid through said first duct, said delivery valve member and said flow control valve member being positioned within said third chamber for controlling the flow of fluid through said second duct, said push-rod means being slideably received within said second duct for coacting with said suction valve member and said delivery valve member;

said valve block further having a first valve seat formed thereon within said second chamber adjacent said first duct for permitting said suction valve member to 7 sealingly engage same and prevent flow of fluid through said first duct; and

said valve block further having a second valve seat formed thereon within said third chamber adjacent said second duct for engagement therewith by said delivery valve member for preventing fiow of fluid through said second duct.

4. An elevating unit according to claim 3, wherein the flow control valve member comprises a sleeve freely and slideably positioned Within said third chamber, said sleeve being open at one end and having a base substantially closing said sleeve at the other end, said base having a small orifice extending therethrough, and spring means urging said sleeve in a direction away from said second valve seat with said sleeve being movable in opposition to said spring means so that said one end can be applied in a fluid-type manner around said second seat.

5. An elevating unit according to claim 4, wherein the delivery valve member comprises a ball valve positioned adjacent the one end of the sleeve and movable inside the sleeve when the sleeve moves into sealing engagement around the second valve seat, said spring means being interposed between the ball valve and the base of the sleeve for urging the ball valve into sealing engagement with said second valve seat.

6. An elevating unit according to claim 1, wherein the recess formed in said housing comprises a cylindrical counterbore opening outwardly through a surface of the housing, said counterbore having an internal threaded portion adjacent the opening said valve block comprising a sleeve-like member of circular cross section with said valve block being freely slideably received within said cylindrical counterbore and said securing means including a threaded screw member threadably received within the opening of said counterbore and in abutting engagement with said valve block for maintaining same in position within said housing; and said suction valve member, said delivery valve member and said flow control velve member being confined wthin the interior of said sleeve-like member whereby said valve hlock including the valve members therein can be removed from said housing as a unit.

References Cited UNITED STATES PATENTS 2,322,314 6/1943 Pomeroy.

2,398,558 4/1946 Reimuller.

2,550,163 4/1951 Phenning.

2 ,791,028 5/1957 Bidin.

3,081,007 3/1963 Lightburn.

2,815,646 12/1957 Swanson.

3,045,653 7/1962 Colgan 91454 3,072,144 1/1963 Cassell 91447 3,202,233 8/1965 Doplin.

CARROLL B. DORITY, JR., Primary Examiner US. Cl. X.R. 

